This invention relates to a vacuum operated sewerage control system and particularly to such a system employing control apparatus adapted to be mounted below ground level.
A functional vacuum operated sewerage collection system employs a vacuum collection station connected to the terminal end of a pipe network of sewer lines which may extend outwardly a distance of several miles. Each sewerage inlet point, typically serving one or two houses, includes a valve and controller assembly providing intermittent feed of sewage into the vacuum pipe network in the form of a slug of sewage followed by atmospheric air. The sewage slug moves at a high speed through the pipe due to pressure differential of vacuum pressure in front and atmospheric pressure behind it, as far as the slug fills full cross-section of the pipe and therefore, creates a seal in the pipe. The slug movement eventually stops as the pressure differential diminishes after the inlet valve has been closed and also due to the fact that the sewage slugs falls apart by friction and doesn't fill the full cross-section of the pipe. The slugs are collected and reformed in pockets created in the sewerage pipe and during the next operating cycle of the inlet valve and controller combination a new slug of sewage with atmospheric air behind it enters the system and the pressure differential is again created and thus, all slugs in the reforming pockets of the sewage line move certain distance forward. This cycle of forming and transport for a distance, disintegration, reforming, etc. is repeated every time an inlet valve and controller combination goes through its cycle and lets a slug of sewage and atmospheric air into the vacuum supplied sewage pipe network.
A particularly satisfactory controller assembly is disclosed in U.S. Pat. No. 3,791,397 which issued Dec. 11, 1973 to George J. Janu, wherein the vacuum in the sewerage line is employed as the source of operation energy for the valve and controller assembly. A hydrostatic pressure sensor is mounted immediately upstream of the discharge control valve. The operating pressure supply is connected to the flow line downstream of the main discharge valve through a regulator providing reference vacuum independent of the flow line vacuum, at least to a minimum vacuum condition. A fluid timing network connects the sensor to one side of a comparator, the opposite side of which is connected to the output of the regulator. A time delay is thus introduced to prevent response to temporary pressure changes such as shock conditions. The comparator drives a fluid timing capacitor which interconnects the output of the comparator through a suitable fluid switch to a pilot valve for controlling the main discharge valve. The sensor actuates a timing means to establish discharge flow for a predetermined time after which the system resets to standby to subsequently respond when the light level again establishes a signal indicating a high limit. The timing means provides a constant volume of the liquid discharged per cycle into the system. The pilot valve is constructed to produce a break-before-make switching operation to establish a reliable transfer of an operating pressure signal to the main discharge valve for actuating thereof for discharge.
The main valve unit is a piston operated plug valve positioning an elastomer seal member relative to a valve seat and positively closed by the spring force and the system vacuum. The piston operator is mounted on a coupling elbow of the plug valve and includes a piston rod slidably mounted in a liquid tight seal. The piston rod is connected to a cup-shaped piston and rolling diaphragm mounted within an operator cylinder, with atmospheric air and vacuum selectively impressed on the cylinder for opening and closing the valve. The controller is conveniently mounted on top of the operator and connected to the sensor and to the vacuum line for operating power to provide a compact and integrated inlet valve and controller assembly.
The inlet valve controller assembly is typically located in a covered pit several feet below ground level for direct in-line connection in the sewer pipe. The air intake pipe or pipes are brought out of the pit and located to prevent entrance of rain and/or ground water.
The several operating and control components are however often subjected to operation in submerged water conditions. As a result of heavy rain, locations having relatively high water tables and the like, the control pit may contain water levels submerging the valve and controller assembly. Although the system component can be constructed reasonably liquid tight, there is always the probability of some leakage within a practically constructed enclosure, at the tubing connections and the like. The use of vacuum pressure within the several chambers of the control assembly, of course, tends to promote leakage and makes the problem even greater.
The entry of water into the control assembly generally interferes with the optimum functioning of the system particularly over relatively long periods of time. The presence of water, for example, interferes with the free movement of the moveable components, either slowing them down or in extreme cases preventing movement. This, of course, results in a malfunctioning. Water, of course, may also cause relatively significant corrosion of the valve and controller components, resulting in malfunction of the assembly.
A significant problem associated with the presence of water within the system arises as a result of surface tension of water slugs within the lines and components, functioning to restrict or prevent proper airflow through the system. For example, an air filter is normally provided in the air intake line. This fine filtering media normally is constructed with openings on the order of 0.7 microns. If water wets the fine filtering media, the surface tension may be such as to block the filtering openings, preventing proper supply of air.
The surface tension characteristic of water within the system may similarly block free air flow through the small internal diameter tubing, air flow restricting orifices and the like. The required air flow is again prevented with a resulting improper functioning of the controller system.
In addition, the assembly is subjected to various other possible sources of water.
Water may be introduced into the various operating components as a result of the continous flow of atmospheric air supplied through the sensor and the controller during standby. When the sensor triggers a flow cycle, a substantially higher intermittent atmospheric air flow is supplied to the piston operator to effect the opening and closing of the main valve. During those periods of the year when the ambient or atmospheric air is relatively warm, the air is at a high relative humidity, with a consequent high moisture content. The subterranean valve and controller assembly is relatively cool. The atmospheric air is drawn into the several chambers and as a result of a heat transfer between the air and the cold structure elements, the air temperature approaches the temperature of the elements. The cooling of the hot, moist air rapidly drops its temperature, normally below its dew point. As a result, rapid saturation of the intake air with moisture is created, with the excess moisture condensing onto the elements of the valve and controller assembly. The particular amount of condensation, of course, depends upon each particular installation, particularly ventilation, depth, geographical location, prevailing weather conditions and the like. However, in many installations, the quantity may be of such a level, particularly if there is any other leakage, that a malfunction or less than desireable function of the assembly is obtained.
Further, the flow through the main sewer line and the main valve unit provides a further possible source of introduction of water and foreign matter into the control assembly. For example, the vacuum operated assembly is connected to the vaccum supply side of the main valve. The flow conditions in a sewer pipe are generally of a relatively high velocity and turbulent characteristic at the time of main valve opening. There is a significant probability that water and sewage from the main sewer line may enter the vacuum supply connection or port and enter into the valve controller assembly. Further, upon opening of the main valve, a rapid decrease in the level of vacuum on the vacuum side of the valve results. A momentary condition may occur with the vacuum inside the controller higher than at the connection point to the sewer line. Such resulting pressure differential tends to introduce water and sewage into the controller assembly.
In some installations, the downstream water sewer line may slope downwardly toward the valve and controller assembly. When the main valve is closed, the hydrostatic pressure associated with the accumulation of water and sewage may force sewage into the vacuum supply connection. The sliding seal of a piston rod operator, of course, forms a further possible leakage location. Mistakes during installation and even after installation, such as an accidental momentary location of the end of the air tube in water, or erroneous installation in a ground plane water location, will introduce water into the assembly.
Thus, the inventors have discovered that the presence of water within the internal components generates problems and is a distinct source of malfunction of the vacuum operated system. Such water may arise as a result of the buried location of the valve and controller assembly, moisture in the intake air condensing within the operating and control components, the operating pressure conditions and finally leakage conditions within the assembly due to normal manufacturing tolerances, erroneous workmanship or the like.